The invention relates to a safety device for an automotive pneumatic system, including a safety valve that includes a restoring element. The invention further relates to a method for operating an automotive pneumatic system in a safety mode. During normal operation, the pressure-regulator valve, regeneration valve and circuit-protection device components can be actuated. In the safety mode, at least one of the components fails to function.
U.S. Pat. No. 5,678,900 discloses a pneumatic system having a pressure regulator, a regeneration device, a circuit-protection device and a safety valve. The system serves to release compressed air when a magnet valve in the pressure regulator actuates a piston of the safety valve.
A drawback of such a system is that during currentless operation of the system, the compressor or the compressed-medium source is no longer regulated, and must operate counter to a maximum pressure, namely the safety-valve pressure of the safety valve of the pressure regulator. The safety-valve pressure of such a system is high, e.g., it must be higher than the maximum value of the pressure regulator. This can be harmful to the compressors, and may cause damage to valve devices that must be supplied directly with the safety-valve pressure, i.e., the initial pressure of the pressure-regulator valve, during currentless operation.
It is an objective of the present invention to disclose a safety device for an automotive pneumatic system, which is intended to prevent the compressor or the compressed-medium source from operating counter to an excessively-high pressure during currentless operation or in the safety mode, such as when electrical faults occur or when a plug breaks or the like, that is, particularly when at least one component fails. The present invention particularly assures less stress on the compressor or the compressed-medium source and the valve devices. It is a further objective of the present invention to disclose a corresponding method, with which it is possible to operate in a safety mode without greatly stressing the compressor and the valve devices.
The objective is accomplished by a safety device for an automotive pneumatic system that includes a safety valve having a restoring element with an adjustable restoring force. This measure allows the pneumatic system safety-valve pressure in the safety mode or currentless mode to be set lower than the safety-valve pressure in the normal operating mode, that is, when current is supplied.
If the restoring force of the restoring element can be adjusted by means of a pressure, and/or mechanically, which is preferable, this permits a simple, preferred embodiment in which existing elements of the pneumatic system can be utilized. The pressure can preferably be adjusted by way of a regeneration valve. For example, the regeneration valve can be set to deventilate a portion of the pneumatic system in the safety mode, or currentless mode—especially the portion acting on the restoring element. If the pressure acts on the restoring element via a piston or a diaphragm, as is preferable, this allows for an especially simple embodiment of the invention.
The restoring element is preferably a spring. Furthermore, the safety valve can preferably be actuated by a safety-valve piston, particularly in the normal operating mode.
An automotive pneumatic system is preferably provided with a safety device of the above-described type. A vehicle is also preferably provided with the above-described pneumatic system.
In accordance with the invention, a method for operating in the safety mode of an automotive pneumatic system, in which the pressure-regulator valve, regeneration valve and circuit-protection device components can be actuated in the normal operating mode, and at least one of the components fails to function in the safety mode, is characterized in that the restoring element of the safety valve is relieved or discharged in the safety mode. This method of the invention can be employed to easily accomplish the objective of avoiding heavy stressing of the compressed-medium source or the compressor, and the valve devices in the safety mode or the currentless mode, because the actuation pressure of the safety valve, i.e., the safety-valve pressure, can be set lower than in the normal operating mode.
The regeneration valve is preferably shut-off in the safety mode, causing the rear side of an element that acts on the restoring element to be deventilated. This preferred method step allows the restoring element to be relieved relatively simply, which in turn reduces the safety-valve pressure.
The invention is described below, without limiting the general inventive concept, by way of exemplary embodiments with reference to the drawings; reference should be made to these drawings for all of the inventive details not expressly described in the text.